Long URLs are simply hard to pass along. The links tend to sometimes break in emails, are harder to verbalize in a conversation, and they are difficult, or in some cases, near impossible to remember.

For example, let's say you are visiting a site about how "Experts discover major Internet flaw"

http://www.upi.com/Top_News/2008/07/09/Experts_discover_major_Internet_flaw/UPI-83691215616576/

You can make this link something more useful, such as . . .

http://www.smallsizeurl.com/flaw/

This new Small Sized URL can now be easily remembered and passed along to your friends!